1. Field of the Invention
The present invention relates to a differential amplifier circuit, and more particularly, to a differential amplifier circuit having improved linearity, and a mixer circuit including the differential amplifier circuit.
2. Background of the Related Art
A RF circuit consisting of a single-ended circuit is weak in problems, such as signal coupling or even order distortion, in a higher integrated circuit such as SOC (System on a Chip). In order to solve these problems, a differential circuit is employed. That is, the differential circuit is effective in solving the aforementioned problems since it has high CMRR (Common Mode Rejection Ratio) and IIP2 (Input 2nd Intercept Point).
Further, in the RF circuit, the linearity is a very important factor. This has a close relation with a secondary differential coefficient (gm″) of the transconductance of the amplifier circuit.
The applicant of this application filed a patent application, Korean Patent Application No. 10-2001-0003277, entitled “Single-Ended Differential Circuit Using Complementary Element” filed on 2001 in order to improve the linearity, and was issued with U.S. Pat. No. 6,693,493. Korean Patent Application No. 10-2001-0003277 and U.S. Pat. No. 6,693,493 relate to a method of offsetting the secondary differential coefficient (gm″) of the transconductance using a secondary transistor.
Korean Patent Application No. 10-2001-0003277 and U.S. Pat. No. 6,693,493 disclose a circuit of a single-ended type. “Second-Order Inter-modulation Mechanisms in CMOS Downconverters, IEEE, J. of Solid State Circuits, vol. 38, No. 3 March 2003, pp 394-406”, discloses that there are problems in that high CMRR and IIP2, which are the advantages of the above-described differential circuit, cannot be obtained if the method disclosed in Korean Patent Application No. 10-2001-0003277 and U.S. Pat. No. 6,693,493 are simply applied to a differential circuit.